A mulching film is usually used for the purpose of maintaining moisture in soil, raising underground temperature and the prevention of a loss of fertilizer components, and so on. The mulching in the summer season is effective for the maintenance of moisture in soil and the prevention of a loss of fertilizer components, but the underground temperature is unfavorably increased, which is not desirable for plant plantation. This increased underground temperature causes the problem of a significant propagation of weeds.
The most popular mulching film is a transparent polyethylene film, but when this mulching film is used in the summer season, due to the transmission of sunlight, the underground temperature becomes too high, and weeds propagate too significantly. Thus it is not suitable for crop culture. Although a black mulching film is effective for the inhibition of weeds, it absorbs sunlight well, which causes a raising of the underground temperature, and is not suitable for thus this type of film the lowering of the underground temperature.
To improve the above drawbacks, it has been proposed to use, as a mulching film suitable for the summer season, a white mulching film containing titanium dioxide or a silver polyethylene film containing aluminum powder. These mulching films, however, are still not satisfactory for lowering the underground temperature or preventing the propagation of weeds. Thus, a mulching film satisfying both requirements is not presently available.
In some crop cultures, there are used films obtained by depositing with aluminum or by laminating an aluminum foil on a polyethylene film, but when these films are applied to, the aluminum deposition or aluminum foil is occasionally peeled off or oxidized and fall to tatters during use. They are also expensive. Accordingly, these films are not popularly used. Moreover, a white and black laminate mulching film is also proposed (cf. Japanese Utility Model Publication (Kokoku) No. 38369/1980), but it is still insufficient for lowering the underground temperature in the summer season, while it is effective for the prevention of the propagation of weeds.
It is also known that the above mulching films are somewhat effective for the prevention of various insect pests harmful for the crop culture, such as thrips (e.g. Thrips palmi), aphides (e.g. Aphis gossypii, Mizus persieae), fruits flies (e.g. Zeugodacus cucurbitae), Aulacophora femoralis, etc., but they are not so effective for some insect pests.